1. Field of the Invention
The present invention relates to a communication method of a mobile communication system. More particularly, the present invention relates to a communication method when a mobile station receives a signal from a base station in the mobile communication system by diversity reception.
In addition, present invention relates to a mobile station which carries out communications according to the communication method.
2. Description of the Related Art
FIG. 1 shows an example of a conventional mobile communication system.
As shown in FIG. 1, this mobile communication system is configured by a hierarchical structure wherein radio network controllers 60, 80 control a plurality of base stations 40, 41, 42, 43 which are placed in communication service areas and a switch 100 controls the radio network controllers 60, 80.
For example, a mobile station 18 which resides in a wireless zone of the base station 43 communicates with the base station 43 and communicates with another mobile station via the radio network controller 80, the switch 100 and a predetermined network (which is not shown in the figure).
The mobile station 18 receives a signal from the base station 43 according to the antenna diversity reception method for example. According to the antenna diversity reception method, the error rate of received signals at the mobile station 18 can be decreased by synthesizing signals received by a plurality of antennas and by selecting a signal which is received by an antenna which is in better receiving condition.
In addition, the mobile station 19 which resides in a boundary part between the wireless zone of the base station 40 and the wireless zone of the base station 41 receives signals from the base stations 40, 41 according to a site diversity reception method. According to the site diversity reception method, the mobile station 19 receives same signals each of which signals are sent by the base stations 40 and 41 respectively. Then, the mobile station 19 synthesizes and selects the signals so that the error rate can be decreased.
In the communication method according to the antenna diversity reception method, the interval between antennas becomes smaller as the mobile station (a cellular phone and the like) becomes smaller. As a result, the correlation between receiving systems connected to the antennas becomes high so that large effect of diversity can not be expected.
According to the site diversity reception method, when the mobile station resides in a boundary part of the wireless zones, the effect of the method can be obtained. However, when the mobile station resides in a central part of a wireless zone of a base station, attenuation of signals from another base station becomes large so that the effect of the diversity reception can not be obtained. Thus, it is necessary to install base stations in higher density for realizing effective site diversity reception. That is, it is necessary to increase the number of base stations which should be installed in the communication service area so that a cost of communication equipment increases.